HY8:South Dakota Concrete Box

HY-8 Version 7.3 and later has coefficients for computing inlet control depths using research contained in FHWA Publication No. FHWA-HRT-06-138, October 2006: Effects of Inlet Geometry on Hydraulic Performance of Box Culverts.

Overview and implementation

The document "Effects of Inlet Geometry on Hydraulic Performance of Box Culverts" (FHWA Publication No. FHWA-HRT-06-138, October 2006) describes a series of tests that were performed to obtain design coefficients for various inlet configurations on reinforced concrete box culverts. The following variations in inlet configurations were tested: wingwall and top edge bevels and corner fillets, multiple barrels, different culvert span-to-rise ratios, and skewed headwalls. The results of the tests were K, M, c, and Y inlet control design coefficients and 5th degree polynomial coefficients (required by HY-8) that were given in the FHWA document. The 5th degree polynomial coefficients given in the FHWA document cannot be used directly in HY-8 because the coefficients were only developed for a HW/D range between 0.5 and 2.0. HY-8 requires the polynomial coefficients to be valid between HW/D values of 0.5 and 3.0. Therefore, the polynomial coefficients had to be re-computed using the K, M, c, and Y coefficients from the FHWA report.

Several recommendations were made at the end of the FHWA document. Since the recommendations were a consolidation of the FHWA research, these recommendations were used in HY-8. The recommendations consolidated the results of the South Dakota box culvert testing into 13 different sets of coefficients, called "Sketches", which represent different inlet conditions. The HY-8 developers further consolidated the results into 10 sets of inlet edge conditions that were added as a "South Dakota Concrete Box Culvert" type in HY-8.

For information on the exact coefficients used and to view diagrams showing the different culvert configurations that were implemented in HY-8, see the help describing the HY-8 South Dakota Concrete Box polynomial coefficients.